Background Information - The Kinetic Molecular Theory (KMT)
The Kinetic Molecular Theory explains the structure and nature of matter by postulating that:
All matter is composed of very small particles
All particles are in constant motion (they have kinetic energy)
Particles are separated by empty space.
All particles are mutually attracted to each other (intermolecular forces)
When particles collide, kinetic energy is conserved (no energy is lost or gained from the system)
We are all aware of the four states of matter – solids, liquids, gases and plasma. Excluding plasmas (behave like gases), each state has observable characteristics:
Characteristic
Solids
Liquids
Gases
Shape
Defined
Variable
Variable
Volume
Defined
Defined
Variable
Compressibility
No
Very Slight
Highly
Density
High
High
Low
Flows
No
Yes
Yes
The statements of the KMT explain these observations.
Solids
Energies of individual solid particles are insufficient to overcome intermolecular forces.
Particles are held close together in a lattice structure. They vibrate about a fixed position.
Liquids
Particles have relatively more energy and are therefore not so tightly held to their neighbours.
Particles are not fixed in position and rotate about one another (ie flow)
Gases
Particles have high energies and can break away from intermolecular forces.
Particles are free to move about (translate). The spaces between particles are extremely large relative to the particle size.
Particles have kinetic energy (KE), a function of motion, and potential energy (PE), a function of relative position. Temperature is a measure of the average KE of the particles. If temperature is increasing,KE is increasing. PE is associated with the changes in particle position that accompany a change of state. The sum of both energies reflects the total internal energy of the particles in a substance.
Kinetic Molecular Theory and Ideal Gases
The IB syllabus is concerned with a more academic look at the KMT as it applies to ideal gases
A gas consists of a collection of small particles traveling in straight-line motion and obeying Newton's Laws.
The molecules in a gas occupy no volume (that is, they are points).
Collisions between molecules are perfectly elastic (that is, no energy is gained or lost during the collision).
There are no attractive or repulsive forces between the molecules.
The average kinetic energy of a molecule is 3kT/2. (T is the absolute temperature and k is the Boltzmann constant.)
It is extremely important that you understand that individual gas particles in a sample can have very different amounts of KE. It is the average KE of the entire sample that is reflected by a temperature measurement. The distribution of particle KE/speed is depicted in a Maxwell Boltzmann plot.
For some background information (the reference source for this page) on KMT and Ideal Gases click here.
The Kinetic Molecular Theory explains the structure and nature of matter by postulating that:
- All matter is composed of very small particles
- All particles are in constant motion (they have kinetic energy)
- Particles are separated by empty space.
- All particles are mutually attracted to each other (intermolecular forces)
- When particles collide, kinetic energy is conserved (no energy is lost or gained from the system)
We are all aware of the four states of matter – solids, liquids, gases and plasma. Excluding plasmas (behave like gases), each state has observable characteristics:Solids
- Energies of individual solid particles are insufficient to overcome intermolecular forces.
- Particles are held close together in a lattice structure. They vibrate about a fixed position.
Liquids- Particles have relatively more energy and are therefore not so tightly held to their neighbours.
- Particles are not fixed in position and rotate about one another (ie flow)
GasesParticles have kinetic energy (KE), a function of motion, and potential energy (PE), a function of relative position. Temperature is a measure of the average KE of the particles. If temperature is increasing,KE is increasing. PE is associated with the changes in particle position that accompany a change of state. The sum of both energies reflects the total internal energy of the particles in a substance.
Kinetic Molecular Theory and Ideal Gases
The IB syllabus is concerned with a more academic look at the KMT as it applies to ideal gasesIt is extremely important that you understand that individual gas particles in a sample can have very different amounts of KE. It is the average KE of the entire sample that is reflected by a temperature measurement. The distribution of particle KE/speed is depicted in a Maxwell Boltzmann plot.
For some background information (the reference source for this page) on KMT and Ideal Gases click here.